The effect of lateral bracing on the dynamic response of wood floor systems

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Virginia Tech

This thesis presents the results of an extensive study of several types of lateral bracing for solid-sawn and parallel-chord truss floor systems. Three solid-sawn floor bracing systems were evaluated: X-bridging, full-depth solid blocking, and finally, post-tensioned solid-blocking. Five different truss bracing systems were investigated: bottom-chord bracing, steel X-bracing, strong-back bracing, and the bracing combinations of X-plus bottom-chord bracing, and strong-back plus bottom chord bracing were evaluated. A total of seven, 4.9m x 4.9m floor specimens were constructed. Four 38 x 286 mm (2 x 12 inch nominal), solid-sawn wood joist floors were constructed for evaluation of the solid-sawn bracing systems. Three 305 mm (12 inch) deep, bottom-chord bearing, metal plate connected, parallel-chord truss floors were constructed to evaluate the truss floor bracing systems. Both floor systems utilized joist/truss spacings of 610 mm (24 inches) on center, and were covered with 18.3 mm (23/32 inch) thick, tongue-in-groove, plywood sheathing. The bracing systems were evaluated at different live load levels and boundary conditions.

The bracing systems were subjected to both static and dynamic loadings. The effect of the bracing systems were determined based on four parameters: one static, and three dynamic. The percent change in concentrated load carried by the loaded joist was used as the static test parameter. The effect, if any, of the bracing systems on the modal resonant frequencies, separation of frequencies, and damping characteristics of the floor systems, were used as dynamic parameters. Future research and design recommendations were given in the conclusion chapter.